Kinetic and Thermodynamic Studies of Chromium (VI) Biosorption on Sporosarcina Pasteurii

European Journal of Scientific Research

ISSN: 1450-216X / 1450-202X Vol. 95 No 1 January, 2013, pp.50-62

© EuroJournals Publishing, Inc. 2012

http://www.europeanjournalofscientificresearch.com

Kinetic and Thermodynamic Studies of Chromium (VI)

Biosorption on Sporosarcina Pasteurii

K. Chithra

Tamil Nadu Pollution Control Board, Chennai, India

E-mail Address: [email protected]

Anil Mapari

Department of Biotechnology, SRM University

Kattankulathur, Chennai, India

M. Somasundaram

Tamil Nadu Pollution Control Board, Chennai, India

Lima Rose Miranda

Department of Chemical Engineering

A.C.Tech, Anna University, Chennai, India

Abstract

The removal of toxic heavy metal ions from wastewater is of great importance. In

this study, the biosorption of Cr(VI) ion onto Sporosarcina pasteurii was investigated in

the batch mode by considering the effects of various parameters like pH, contact time,

initial concentration and temperature. Optimum adsorption of Cr (VI) took place at the pH

value of 4.0, biomass dose of 0.8 g and temperature of 303K. Equilibrium isotherms,

kinetic data, and thermodynamic parameters have been evaluated. Equilibrium data agreed

well with the Langmuir isotherm model. The kinetic data was found to follow the pseudo-

second-order model. The thermodynamic parameters Gibbs free energy (∆G◦), enthalpy

(∆H◦), and entropy (∆S◦) changes were also calculated. The numerical values of

thermodynamic parameters indicated the exothermic nature, spontaneity and feasibility of

the sorption process. Further, the biosorbent was characterized by Fourier Transform

Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). FTIR studies

indicated the involvement of various functional groups present on biomass surface in the

sorption of Cr(VI).

Keywords: Biosorption, Chromium (VI), Langmuir, Freundlich

1. Introduction The removal of toxic metal ions from wastewater is an important and widely studied research area.

Chromium (VI) is a hazardous heavy metal found in the effluents of industries like electroplating, the

manufacture of dyes and pigments, wood preserving, textiles, rubbers, leather and cement. In addition,

chromium (VI) has been reported to be carcinogenic to humans (Karthikeyan et al, 2005). Due to the

toxic effect it is necessary to eliminate chromium from the contaminated effluent. Conventional

Kinetic and Thermodynamic Studies of Chromium (VI) Biosorption on Sporosarcina Pasteurii 51

technologies used for the removal of Cr(VI) from aqueous solutions includes reduction (Kim et al,

2002), reduction followed by chemical precipitation (Ozer et al, 1997), adsorption on activated

carbon(Sarin et al, 2006), ion exchange (Rengaraj et al, 2003), lime coagulation, reverse osmosis and

solvent extraction ( Volesky, 2001; Juang and Shiau, 2000; Yan and Virarghavan, 2001), most of these

methods have drawbacks such as high capital or operational cost. Besides the disposal of the residual

metal sludge, it is not suitable for small-scale industries ( Kobya et al, 2005). In such a scenario, the

removal of heavy metal from aqueous solutions by biosorption is a promising and innovative

technology using inactive and dead biomass.

The biosorption technique offers the advantages of low operating costs, reduced amount of

chemical and/or biological sludge to be disposed of and high efficiency in decontaminating effluents

with dilute metal ion content (Brady et al, 1999; Huang et al, 2003; Kumar et al, 2006; Fiol et al, 2006;

Pamukoglu and Kargi, 2006; Mack et al, 2007; Pradhan et al, 2007; Yu et al, 2007; Goksungur et al,

2005). The use of dead microbial cells is more advantageous because they are not affected by toxic

wastes and do not require a continuous supply of nutrients. They can also be regenerated and reused for

many cycles (Vijayaraghavan and Yun, 2008; Gupta and Rastogi, 2008). The biosorption mechanism

depends on the type of functional groups on the surface of the biomass, the nature of the metal and the

characteristics of the matrix around the biosorbent species. However, the exact adsorption mechanism

is not well understood yet. Numerous chemical groups have been suggested to contribute to the metal

binding by bacteria (Mann, 1990). These groups include hydroxyl, carbonyl, carboxyl, thioether,

sulfonate, amine, amide, imidazole, phosphonate, and phosphodiester.

The present work investigates the potential use of Sporosarcina pasteurii biomass as metal

sorbent for chromium removal from the aqueous solution. Optimum biosorption conditions were

determined as a function of pH, biomass dosage, contact time, and temperature. The Langmuir and

Freundlich isotherms were used to describe equilibrium isotherms. Biosorption mechanisms were also

evaluated in terms of their thermodynamics and kinetics. The role played by the functional groups

present in the biomass in sorption was also determined by FTIR and SEM

2. Materials and Methods 2.1. Biomass Preparation and Pretreatment

Gram positive microorganism Sporosarcina pasteurii (2477) used for the study was purchased from

National Collection of Industrial Microorganisms (NCIM), Pune, India. The Bacterial strain was

preserved on nutrient agar slants and sub cultured every four weeks. This strain was grown in nutrient

medium and appropriate proportion was used for the experiment. Standard sterile techniques were used

for the inoculation of culture. Medium used for the microorganism and all the glassware were properly

sterilized in an autoclave at a pressure of 15 psi and 121ºC for 30 minutes. Loop full of bacterial

culture was taken from the nutrient agar slants and used as an inoculum for 150 ml nutrient broth (seed

culture). After an overnight incubation at 120 rpm and 30ºC, 10% of this seed culture was used for

inoculating 1000 ml nutrient broth in Erlenmeyer flask. The inoculated flask was incubated in an

orbital shaker at 120 rpm and 300C for 2 days to obtain the biomass. After the incubation, biomass was

centrifuged at 10,000 rpm for 10 minutes. The supernatant was discarded and the cells were re-

suspended in water for washing and again centrifuged as above to make sure that no media remains on

the cell surface. The biomass was heat killed in a conventional hot air oven at 60 oC for 24 hrs. This

biomass was used for the sorption experiment.

2.2. Chromium Solution and Analysis

The stock solution of Cr (VI) (1000 mgl−1

) was prepared in deionized water with potassium dichromate

(K2Cr2O7). All working concentration was obtained by diluting the stock solution with deionized water

and the pH was adjusted to the desired value using 1M HCl and 1M NaOH solution. The concentration

of the Cr(VI) ions was determined spectrophotometrically after complexation of the metal ion with 1,5-

52 K. Chithra, Anil Mapari, M. Somasundaram and Lima Rose Miranda

diphenylcarbazide (Eaton et al, 1995). The absorbance was recorded at 540 nm using UV

spectrophotometer (Elico SL 159, India) and concentration was determined from the calibration curve.

2.3. Batch Biosorption Studies

The biosorption experiment was carried out using the batch equilibrium technique at different pH

values (3.0, 3.5, 4.0 and 4.5) and temperatures (20, 30 and 40◦C). Chromium (VI) ions test solutions

were agitated in a shaker at 180rpm for adsorption equilibrium. Equilibrium biosorption study was

performed by using 8g l-1

of the dried biomass. Samples were taken at definite intervals (0, 5, 15, 30,

45, 60, 75, 90,105min) for the residual metal ion concentrations in the solution. Before analysis the

samples were centrifuged at 10,000 rpm for 10 min, and then the supernatant fractions were separated

and analyzed for the remaining metal ions. Isotherm studies were recorded by varying the

concentration of chromium from 10 to 50mgl−1

.The adsorption capacity qe (mgg−1

) after equilibrium

was calculated by the following equation:

m

xVCCmggq eo

e

)()( 1 −

=− (1)

V is the volume of the solution (l) and m is mass of adsorbent (g).

3. Result and Discussion 3.1. Effect of pH on Cr (VI) Biosorption

pH is an important factor affecting biosorption of metal ions. Fig.1 shows the adsorption capacity at

different pH. It can be observed from the figure that the uptake of Cr(VI) increases with increase in pH.

The sharp decrease in adsorption above pH 4.0 may be due to occupation of the adsorption sites by

anionic species like HCrO4-; Cr2O7

2-; CrO4

2-. These species retard the approach of such ions further

toward the sorbent surface (Das et al, 2000; Donmez and Aksu, 2002). However, at pH less than 4.0 a

decrease in adsorption capacity is observed due to the chromium being present predominantly as

H2CrO4.

Figure 1: Effect of pH on adsorption capacity at Initial concentration of 10 mg l

-1; 180rpm; Biomass: 0.8g.


3.2. Effect of Biomass Dosage

The biomass dosage is an important parameter because this determines the capacity of the biosorbent

for a given initial concentration. The effect of biomass dosage for the removal Cr(VI) was studied by

varying the amount of biomass from 0.1 to 1.0 g (100 mL)−1

, while keeping other parameters (pH 4,

agitation speed 180 rpm, temperature 303Kand contact time 90min) constant and is shown in Fig. 2..

The amount of metal ions adsorbed per unit weight of adsorbent (qe) decreases with increase in

biomass dosage (6.6 to 0.92 mg g-1

).This is due to the fact that at higher biomass dose, the solution

metal ion concentration drops to a lower value and the system reaches equilibrium at lower values of

‘qe’ indicating the adsorption sites remain unsaturated.

This is due to the fact that the actual number of active sites per gram of adsorbent does not

increase proportionately and hence there is a regular decrease in adsorption capacity (Helen Kalavathy

and Lima Rose Miranda, 2010).

Figure 2: Effect of biomass dosage on the adsorption capacity at 10 mgl

-1; pH: 4; contact time: 90min;

temperature: 303K

3.3. Effect of Initial Metal Concentration and Time

When the initial metal ions concentration was varied from 10 to 50 mgl-1

at temperature 303K, the

biosorption efficiency of chromium ions to the biomass decreased as the initial concentration of metal

ions was increased (Fig.3). This may be due to the increase in the number of ions competing for the

available binding sites in the biomass for complexation of Cr (VI) ions at higher concentration (Bai and

Abraham, 2003; Puranik and Paknikar, 1999). As can be seen in Fig. 3, the percentage removal of ion

increased with the time of shaking and attained an optimum at 90 min which indicates that the

adsorption tend towards saturation. Hence the contact time of 90 minutes was taken to be the

equilibrium time.


Figure 3: Effect of initial metal concentration and time on percentage removal at pH: 4; 180rpm; Biomass:

0.8gl-1

3.4. FTIR Analysis

One important characteristic of a biosorbent is the presence of surface functional group, which is

largely characterized by the FTIR spectroscopy method. Various researchers have suggested that the

functional groups such as carboxyl, hydroxyl, amide etc. are responsible for biosorption of metal ions

(Park et al, 2005; Tunali et al, 2006), these functional groups are the potential sites for adsorption and

the uptake of metal depends on the various factors such as abundance of site, their accessibility,

chemical state and affinity between the adsorption site and metal. The FTIR spectra of unloaded

Sporosarcina pasteurii and metal loaded Sporosarcina pasteurii biomass in the range of 450–4000cm−1

was performed to find out which functional group is responsible for the biosorption process (Fig. 4). IR

absorption bands and corresponding possible groups are tabulated in table 1. These bands are the

functional groups of Sporosarcina pasteurii which participated in Cr (VI) biosorption.

Figure 4: Infrared spectra of the biomass: (a) before and (b) after Cr(VI) sorption


Table 1: IR absorption bands and corresponding possible groups

Biosorbent Surface functional group Wave numbers

Sporosarcina pasteurii biomass

–OH and –NH stretching 3400

–CH2 asymmetric stretching 2928

–CH2 symmetric stretching 2854

C=O 1654

N–H bending 1458

Sulfamide bonds (SO) 1248

C–O stretch 1021

3.5. SEM and EDAX Analysis

SEM micrographs and EDAX spectra obtained before and after chromium biosorption onto

Sporosarcina pasteurii biomass is presented in Figs. 5-8 these micrographs indicate the presence of

new particles over the surface of chromium-loaded Sporosarcina pasteurii cells confirming the

biosorption phenomenon. This observation was confirmed by EDAX analysis which revealed Cr (VI)

signals together with the presence of gold peaks in all spectra.

Figure 5: Typical SEM micrograph of Sporosarcina pasteurii

Figure 6: Typical SEM micrograph of Sporosarcina pasteurii (Cr (VI) loaded)


Figure 7: EDAX spectra of heat inactivated Sporosarcina pasteurii

Figure 8: EDAX spectra of heat inactivated Sporosarcina pasteurii (Cr (VI) loaded).

3.6. Adsorption Isotherms

Analysis of equilibrium data is important for developing an equation that can be used for design

purposes. Langmuir and Freundlich models have been extensively used to describe the equilibrium

established between metal ions adsorbed on the biomass (qe) and metal ions remaining in the solution

(Ce) at a constant temperature. The Langmuir equation refers to a monolayer sorption onto the surface

containing a finite number of accessible sites:

The mathematical expression of the Langmuir isotherm is given as

max

1

Q bCeq

e bCe

=

+

(2)

The linearization of equation (2) is given as

1

max max

C Ce e

q Q b Qe= + (3)

where Ce is the equilibrium concentration (mg/l) and qe the amount adsorbed at equilibrium (mg/g).

The Langmuir constants Qmax (mg/g) represent the maximum adsorption capacity and b (l/mg) relates

the heat of adsorption.


The Freundlich isotherm is an empirical model relating to the adsorption intensity of the

sorbent towards adsorbent. The isotherm is adopted to describe reversible adsorption and not restricted

to monolayer formation. The mathematical expression of the Freundlich model is 1/n

e F eq K C= (4)

where KF and n are the constants which denotes adsorption capacity and adsorption intensity

respectively. A linear form of the Freundlich model can be written as follows

e F e

1ln q ln K ln C

n= + (5)

A plot of ln qe versus ln Ce gives a straight line with slope KF and intercepts 1/n. The theoretical

parameters of isotherms along with regression coefficients are listed in Table 2. The isotherms are

compared based on the parameter values with experimental data at 303K as shown in Fig. 9. The

isotherm parameters for both the equations along with the values of coefficient of correlation (R2)

(table 2) shows that the data fits the Langmuir equation better than Freundlich equation.

Figure 9: Adsorption isotherms at pH 4.0 and T = 303K

Table 2: Langmuir and Freundlich model parameters at different pH conditions for (VI) by Sporosarcina

pasteurii

pH Langmuir parameters Freundlich parameters

Qmax (mg/g) b (l/mg) R2 KF (l/g) n R

2

3 5.24 0.21 0.996 1.14 2.11 0.984

3.5 5.49 0.22 0.998 1.18 2.02 0.978

4 5.71 0.27 0.999 1.26 1.90 0.964

4.5 5.5 0.23 0.994 1.17 1.98 0.956

3.7. Biosorption Kinetics

In order to study the biosorption kinetics of Cr (IV) ions onto Sporosarcina pasteurii biomass, two

kinetic models, Lagergren’s pseudo-first-order and pseudo-second-order were applied to the

experimental data. The linearized form of the pseudo-first-order rate equation (Karthikeyan et al,

2005), is given as

1e t e

klog(q q ) log q t

2.303− = − (6)


where qe (mgg-1

)denotes equilibrium concentration of Cr(VI)in solution, qt (mgg-1)represents residual

concentration and k1 (min-1

) is first order rate constant the slope and intercept of plot log (qe −qt) versus

t were used to determine the pseudo-first-order rate constant k1. In order to obtain the rate constants

and equilibrium metal uptake, the straight-line plots of log (qe-qt) against t of Equation (6) were made

at different initial metal concentrations (not shown). It was concluded from the R2 values in table 3.

that the biosorption mechanism of Cr (VI) onto Sporosarcina pasteurii biomass does not follow the

pseudo-first-order kinetic model.

Experimental data was also tested by the pseudo-second order kinetic model which is given in

the following form (Karthikeyan et al, 2005).

2

t 2 e e

t 1 1t

q k q q= + (7)

where k2 (g mg-1

min-1

) is the second order rate constant. The linear plot of t/qt versus t for the pseudo-

second order model for the biosorption at 30 ◦C is shown in Fig 10.The rate constants (k2), the R

2 and

qe values are given in table 3. It is clear from these results that the R2 values are very high. In addition,

the theoretically calculated qe values are closer to the experimental qe values. In the view of these

results, it can be said that the pseudo-second-order kinetic model provided a good correlation for the

biosorption of Cr (VI) onto Sporosarcina pasteurii in contrast to the pseudo-first-order model.

Figure 10: Pseudo-second-order kinetics for adsorption of chromium on Sporosarcina pasteurii at 303K

Table 3: Kinetic parameters for chromium biosorption onto Sporosarcina pasteurii at different initial metal

concentrations

C0 (mg/l) (qe)exp

(mg/g)

Pseudo-first order Pseudo-second order

K1 (1/min) qe (mg/g) R2

K2 (g/mg

min) qe (mg/g) R

2

10 1.25 0.008 0.488 0.083 0.045293 1.42 0.992

20 2.5 0.013 1.36 0.378 0.012468 3.09 0.981

30 3.75 0.011 1.42 0.153 0.006514 4.83 0.973

40 5 0.017 3.82 0.905 0.045293 5.3 0.990

50 6.25 0.018 5.61 0.966 0.002726 6.6 0.991


3.8. Effect of Temperature

The adsorption of Cr (VI) onto Sporosarcina pasteurii at different temperatures shows an increase in

the adsorption capacity with the increase in temperature (Fig.11).When temperature is increased from

293 to 323 K, the adsorption capacity increased for the initial concentration of 30 mgl-1

at pH 4.0.

Similar trend is observed for all the other concentrations also. This indicates that the adsorption

reaction is endothermic in nature. The enhancement in the adsorption capacity may be due to the

chemical interaction between adsorbate and adsorbent, creation of some new adsorption sites or the

increased rate of intraparticle diffusion of Cr (VI) ions into the pores of the adsorbent at higher

temperatures (Namasivayam and Yamuna, 1995). The standard Gibb’s energy was evaluated by

ln cG RT K∆ = − (8)

The equilibrium constants Kc was evaluated at each temperature using the following

relationship

AEc

e

CK

C= (9)

where CAE is the amount adsorbed on solid at equilibrium and Ce is the equilibrium concentration. The

other thermodynamic parameters such as change in standard enthalpy (∆H◦) and standard entropy (∆S

◦)

were determined using the following equations

lnc

S HK

R RT

∆ ° ∆ °= − (10)

∆H◦ and ∆ S

◦ were obtained from the slope and intercept of the Van’t Hoff’s plot of lnKc versus

1/T as shown in Fig. 12. Positive value of ∆H◦ indicates that the adsorption process is endothermic. The

negative values of ∆G◦ reflect the feasibility of the process and the values become more negative with

increase in temperature. Table 4 summarizes the result.

Figure 11: Effect of temperature on percentage removal at initial concentration of 30 mg l

-1 pH: 4; 180rpm;

Biomass: 0.8gl-1

.


Figure 12: Plot of ln Kc vs. 1/T for the estimation of thermodynamic parameters for biosorption of Cr (VI) onto

Sporosarcina pasteurii biomass

Table 4: Thermodynamic parameters of Sporosarcina pasteurii at initial concentration of 10mg l

-1, pH: 4

T(K) ∆G(kJ/mol) ∆H(kJ/mol) ∆S(J/mol k)

293 -2.064

22.506 83.78018 303 -2.835

313 -3.742

4. Conclusions The experiments conducted with the biosorption showed that Sporosarcina pasteurii can remove Cr

(VI) by biosorption. It was also observed that the maximum biosorption at pH 4.0. The adsorption

equilibrium data has been fitted very well to Langmuir than Freundlich adsorption model. The sorption

capacity was found to increase with the increase in solute concentration and temperature. The rate of

sorption was found to follow pseudo-second order kinetics. Further from the value of ∆H◦ it is revealed

that the biosorption process is endothermic.

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Nomenclature

b Langmuir adsorption intensity constant (l/mg)

n Freundlich isotherm exponent

C0 initial concentration of Cr (VI) solution (mg/l)

Ce equilibrium concentration (mg/l)

CAE amount adsorbed on solid at equilibrium (mg/l)

qe amount adsorbed at equilibrium (mg/g)

qt amount adsorbed at time t (mg/g)

Qmax maximum chromium uptake (mg g-1

)

k1 first-order rate constant(1/min)

k2 second-order rate constant(g/mg min)

M weight of the adsorbent (g)

∆G◦ standard Gibbs energy of adsorption (kJ/mol)

∆H◦ standard enthalpy of adsorption (kJ/mol)

Kc equilibrium constant

∆S◦ standard entropy of adsorption (J/mol k)

T temperature (K)

V volume of the solution (l)

Kinetic and Thermodynamic Studies of Chromium (VI) Biosorption on Sporosarcina Pasteurii

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